The mechanisms by which the precise patterns of synaptic connectivity are established within visual cortex remain unclear. While activity dependent mechanisms have been demonstrated to play a crucial role in the development of visual cortex, many aspects of visual cortical functional organization, such as orientation and ocular dominance columns, are present before animals have had any visual experience. Thus, before the onset of visual experience, spontaneous activity has been proposed to provide instructive cues for guiding the development of cortical functional architecture. The proposed experiments focus on l) examining the correlational structure of spontaneous neuronal activity within multiple stages of the developing visual pathway including the lateral geniculate nucleus (LGN) and visual cortex, and 2) determining how chronic disruption or modification of these activity patterns alters the development of receptive field properties of visual cortical neurons. This work is made possible by recently developed methods for recording patterns of neural activity within central visual structures of freely behaving animals, utilizing chronically implanted multi-electrode recording arrays. In addition, in vivo chronic stimulation methods will be used to introduce artificially correlated neuronal activity into the visual pathway through the application of periodic bursts of electrical pulses to the optic nerve. These experiments should provide new insight into the role of activity-dependent mechanisms in establishing adult patterns of synaptic connectivity within the brain.